Gas fireplaces are well known and typically include a gas burner positioned beneath a plurality of artificial logs, typically made of a non-combustible material, such as ceramic or cement, to simulate the appearance of natural wood logs. One type of gas burner is the "sand pan burner" in which the gas nozzles are buried below the surface of a non-combustible material such as sand or vermiculite contained in a relatively large shallow pan. The gas permeates and disperses through the material and ignites upon entering the atmosphere, thereby creating an orange/yellow flame dispersed over the bed of material and simulating a bed of glowing embers such as coals or ashes. Other types of gas burners include straight and U-shaped gas delivery tubes and pan-shaped burners comprising a plurality of gas ports to produce flames underneath the logs. The gas ports have been configured as a single slot-shaped port, a single row of circular ports or a plurality of uniformly or symmetrically distributed ports.
A natural wood burning fire has certain characteristics including a non-symmetrically distributed flame in which the flames will typically "flicker" so that one portion of fire has a relatively concentrated flame pattern while another portion has a relatively sparse flame concentration. In addition, some of the flames in a natural fire will be taller and/or wider than other flames and will directly impinge on the logs or will appear to emanate from the logs. The fire will also have a "glowing" bed of coals or embers emitting a smaller flame pattern than the logs.
Conventional gas fireplaces have been largely unsuccessful in simulating the pleasing aesthetic appearance of a wood-burning fire, especially with respect to the natural flickering flame pattern and the non-symmetrical distribution of the fire because many typical gas burner systems produce a homogenous and symmetrical distribution of flames. Since direct impingement of the flame on the artificial logs typically cools the flame and creates a highly inefficient and dirty yellow flame and unacceptable levels of soot and carbon monoxide (CO), attempts to direct the gas flame away from the logs and redistribute the flame concentration including, for example, flame deflectors, have only enhanced the poor simulation of a natural wood fire.
Typical gas burners have other problems in addition to the poor simulation of a natural wood burning fire. Not only are the gas burners relatively expensive to manufacture but the U-shaped and straight gas burners require a relatively complex system of grates and/or pins to insure that the logs are properly positioned and mounted above the gas burner. In other instances, the artificial logs are not interchangeable between gas burners and must be specially manufactured to fit with the specific gas burners. Many gas burners, especially the large pan-shaped burners, are inefficient and poorly designed to have relatively large internal gas plenums. When the fireplace is turned off, the gas remaining inside the plenum is inefficiently burned or otherwise disposed. In other instances, the entire volume of gas may ignite simultaneously to create an undesirable "flash burn" inside the fireplace or, if the flame is extinguished, escape into the room.